why did pull prop planes become more prevelent that pusher prop planes?

Factual Questions
1

Well, I’ll start out by saying that I know very little about aerodynamics. But it seems to me that pusher prop planes (ie planes with props are in the rear) seem much more streamlined which seems to be an advantage in airplane design. The Wright brothers used pusher prop planes for thier first plane, so clearly, I’m not the only one thinking that rearward facing engines have some merit. Yet nearly all prop planes have the engine in the front, or on the wings with the prop pulling the plane.

What happened?

2

The only example I can think of is the Wright Bros. flyer that you mentioned but I would guess maybe the wing in front of the prop disturbs or dampens the air flow.

3

Not being familiar with the theory behind the placement of either, the only thing I could suggest is that if you are “pulling” an airplane with a ‘pull prop’, you’d want to get it into the densest, most relatively undisturbed air as possible, i.e. the front of the aircraft - where the drag and parasite drag hasn’t had a chance to disturb the air.

IIRC, a ‘pushing’ propeller has certain inherent deficiencies (beyond what I’ve mentioned) that up until recently weren’t overcome. . .

Tripler
End point? Undisturbed airstream.

4

WAG -

Pushers are harder to cool than tractors.

(airplane engines (almost all) are “air-cooled” (a misnomer) - you need to move a whole bunch of air over the engine to keep it healthy).

5

I don’t know. But as a pilot, I have to guess.

[ul][li]Most reciprocating aircraft engines were and are air-cooled. Putting the engine in front makes them easier to cool.[/li][li]For a long time, most airplanes had a tailwheel. This is why taildraggers are said to have “conventional” gear – because that was the convention. With the tail low, there would be no room for the prop to spin (and even with a nosewheel design there is some danger of a prop strike).[/li][li]Assuming a non-canard configuration, most of the weight needs to be foreward of the centre of lift. That would mean a lot of ballast to balance a rear-mounted engine, and there’s no sense making an aircraft heavier than it needs to be.[/li][li]Assuming a non-canard configuration, there would have to be twin booms, one on each side of the prop, to hold the empanage; or the engine would have to be mounted high on a pod. Both designs have been built, but twin booms add weight and pods add drag (and pitch moment)[/li][/ul]
That’s just off the top of my head. There certainly were pusher canards all through aviation history. One was a design for a WWII fighter called the Ascender (“ass-ender”, get it?) and the Japanese had a pusher canard design as well. But I think cooling was the main issue, followed by the necessity to create a strong, light, relatively inexpensive design.

6

Cooling is vital, to be sure, but the drive element is more important. If you can offer your prop clean (not turbulent) air, I believe you’ll get more effeciency than the other way around. I’m not an aeronautical engineer, though, and I’m not flying in clean air myself. I’m not sure why I wrote this post. What th’ell do I know? I should hold down the backspace key until this entire post disappears. That’s what I should do. Yup. That’s what I ought to do. That would be the easy way, but no…

7

After reading Johnny L.A.'s post, chalk the cooling reason up to adding it to the front of the aircraft.

Also, after a little digging into my college notes, a propeller generates lift as well as thrust. By putting it into the cleanest, nonturbulent air you can, you can sometimes get a hell of a lot more lift than thrust out of it - i.e. in some cases your propeller “pulls” you through the air versus pushing you.

Tripler
Broomstick would be able to answer this better than I.

8

Ya know… I meant to include putting the prop in relatively undisturbed air…

9

Here’s a couple examples of the pusher prop species:
B-36 Peacemaker
XB-42 “Mixmaster”

Apparently the push prop design remained viable in military aviation until jet engines made them obsolete.

10

I can think of a few reasons.

Cooling, which has been mentioned several times.

Crashworthiness. In a slight nosedown impact, the engine will try to come through the passengers.

The prop will be in disturbed air. This has actually caused prop failure in some canard pusher designs.

Prop clearance is harder to come by in a pusher. Pushers often have long spindly landing gear. Some get over this by mounting the engine higher, over the tail boom. This results in a higher thrustline, and significant pitch changes at different power settings.

Damage from foreign objects (FOD). A pusher prop will catch all the crap kicked up by the gear.

Weight and balance. Some pusher planes are so aft heavy when empty that they will rock back onto the tail.

Cabin heating is harder to accomplish with a pusher engine. Most aircraft heat comes from a duct wrapped around the exhaust pipe, it’s hard to get the air to flow forward into the cabin.

Engine instrumentation and controls require longer runs for wiring and cables, often back through the passenger cabin.

If a pusher engine is mounted high for prop clearance, it may require use of a fuel pump, which is unusual in a high-wing aircraft.

A prop failure can strike other parts of the airplane. I have seen a Rans S-12 with the tailboom almost severed by a damaged prop that virtually exploded.
That’s all I could think of at the moment.

11

Everything posted so far probably is a higher priority consideration, but it occurs to me that a pusher might be a little bit hairier than a puller to bail out of. [sub]chop-chop-chop[/sub]

12

This may be a silly question (IANAP), but wouldn’t a pusher aircraft be less willing to fly straight than a front-engined one? I’m thinking of something along the lines of the castor wheel principle. Imagine a small child pulling a trackless toy train across the living room floor, holding on to the locomotive, then have the child push the train from the caboose. In the second situation, the train will be unlikely to go straight ahead. Would a similar thing be an issue in aircraft design?

13

I have heard this before. Imagine if you were pulling a toy with a string, as opposed to pushing it with a stick. Seems like pulling it would be more stable, right? But it doesn’t really work that way. Just think of it as the stick being connected firmly to the toy you are pushing.

This issue comes up a lot when you get a group of gyroplane pilots together. The vast majority of gyroplanes are pushers, and the few that fly tractors insist that theirs are better because pulling it through the air is better than pushing it.

14

It sounds logical but far more important is having the center of gravity in front of the center of pressure. This gives the “caster effect” you’re thinking of. Loads in airplanes have to be distributed so that center of gravity falls in a narrow range to maintain proper flight characteristics. Among other effects a too far aft CG and a plane becomes less stable. Too far forward and it may not have sufficient maneuverability, it actually becomes too stable.

IIRC one of the problems with the B-36 was assymetric load on the props with high pressure below the wing and lower pressure above it.

15

Joey G had a pretty good list. I’d add that if you put the prop right behind the passengers as in the Cessna 337 or various seaplanes, you have to either make twin booms to the tail, or you have to mount the engine up high to clear the rear fuselage structure. And that can cause strange problems because the prop blast misses the tail in some attitudes, but not in others. A few pusher homebuilts have had really squirrely handling characteristics from that. Takeoff in some of these planes can be really strange, and they have a tendency to be ineffective until a higher speed, when they suddenly want to over-rotate.

And if you put the prop aft of the tail like the mini-IMP or the Cirrus VK-30, you need a long, heavy driveshaft that also needs to be perfectly balanced.

16

Arguing about pushers vs. pullers is a lot like arguing canards vs. non-canards. Lots of bandwidth and devotees, but not always real substance.

I’m not an engineer and I don’t have a fancy degree in aerodynamics but I did have my flying start in pushers rather than pullers. The first two years I flew as a pilot it was exclusively in pushers.

While pushers (and for that matter, canards) have the distinction of dating back to the Wright Flyers, there was one very basic problem with them that resulted in a lack a popularity in the first third of the 20th Century.

Although it seems incomprehensible to us today, from 1903 through the 1930’s pilots expected things to go wrong on a fairly regular basis. Engine failures - and therefore forced landings - were not a constant feature but they did happen and pilots expected they would experience them from time to time. In a crash, if you were flying a puller the engine was between you and the ground, meaning the airplane (a contraption of wood and cloth mostly in those days) tended to land on the engine (a big hunk of hot metal). In a pusher, YOU were first at the scene and the engine tended to land on the airplane, and you. There were a number of disturbing instances where the forced landing would have been survivable except for the engine having squashed the occupants. In those early years, where you did find pushers the engines tended to be mounted out on the wings so that if they did break free in a crash the pilot wasn’t between them and the ground (in the original Wright Flyer the engine was offset - the pilot lay down beside it, not in front of it.)

Even today, this is taken into consideration. Some designs put up with thrustline difficulties to mount the engine high enough so that in the event of an accident it will tend to sail over the head of the occupants instead of into them. I do know someone where just that happened to them - a sudden stop, with the engine swinging over their head. Which, of course, means the prop is getting closer. He wasn’t hurt, but he did get the crap scared out of him. I can’t repeat what the guy said (except in the Pit) but his next airplane was a puller.

A lot of the other concerns come down to airplane design. There is no such thing as the “perfect airplane”. Some are better suited to some jobs than others, is all.

Some advantages of a pusher:

Improved airflow over the tail means, on average, better handling (when the engine is running…). Yes, there can be problems with handling at low speeds - ditto for t-tails using traditional puller engines. Any aircraft, even a glider, has to be designed to handle the air flows at various speeds. I’m sure if the majority of airplanes were pusher canards we’d be moaning about the “weird airflows” on a puller non-canard.

More accurate ram air for the pitot tube - that means your airspeed indicator tends to be more accurate over a wide range of speeds. Yes, pullers can have accurate airspeed indications, too - but the placement of the pitot can be tricky.

If you’re open cockpit, a pusher (behind you) doesn’t interfere with the air stream, allowing a direct experience of the relative wind and airspeed by the pilot. If you’re flying with minimal instruments (which is how I started) or even NO instruments (they do quit working sometimes) this is a good thing.

Those tail booms - having two booms around the prop makes it less likely some lineman or passenger will accidently walk into a spinning prop. (This is an exceedingly messy accident no one ever wants to see) It’s not impossible to be that foolish, it just cuts down on the likelihood. Which is a good thing.

Some disadvantages:

Pushers tend to pitch down when powered up, and pitch up when powered down or abruptly failing. This is the opposite of the tendencies you want in an aircraft.

Props can and have severed tailbooms. Unless you have a parachute, this is uniformly fatal.

That whole squash-you-like-a-bug problem in crashes. Since aircraft engines of a given horsepower have become smaller and lighter, and attachment devices stronger, this is not as much an issue as it was in 1920 for very small aircraft. However, there is an upper limit beyond which the engine block will tend to go its own way in an accident.

Crap going through the prop. Granted, crap can go through a front-mounted prop, too - but that’s generally problems on the ground with kicked-up debris and/or birds aloft. Pushers have those two problems AND the additional factor that stuff falling off of or out of the airplane can go through the pusher prop. And stuff DOES fall off and out. Had a friend who’s pusher lost an engine bolt, which took a piece of prop blade off as it departed the airplane. This was a Bad Thing (although I’m happy to say he landed safely) Back when I was flying open cockpit pushers making sure stuff was secured was a major major concern.

Those cooling issues:

Back in the bad old days when everything was out in the open this wasn’t as much of an issue. It’s when you start enclosing the engine in a streamlined cowling that it becomes a problem. In honesty, overheating IS a concern with a covered engine and back in the bad old days the difference in keeping the powerplant cool was enough to reinforce the move from pushers to pullers already started by the crash issues. With the modern ultralight and homebuilt pushers I have seen water-cooling and radiators used to solve that problem. Yes, it adds weight but remember that the modern small aircraft engine is much more efficient than what was used 80 years ago. The 1903 Wright engine was what? 12 horsepower? Weighed a couple hundred pounds? A 50 hp engine is available that is small enough for one person to lift (alright, it’s kinda heavy, but…). Ultralights and homebuilts can lift a payload equal to their own empty weight off the ground and still fly better that what was aloft in 1920. These days, we can afford the extra couple pounds to keep the engine cool, which they couldn’t do 80 years ago.

Those airflow issues:

Here we’re getting into areas where I don’t have a lot of expertise. I can see where airflow can be an issue, that makes sense to my pilot’s eye. But airflow issues are always present - the airflow over the fuselage always affects the tail surfaces, which are vital in most aircraft (canards being the exception) and must therefore be accounted for regardless of engine location.

My experience has been that, with the exception of the pitch tendencies already mentioned, there’s not a heck of a lot of difference from the pilot’s viewpoint. All this squirrelliness I hear rumors about is just that - rumors. Yes, there are some horrifically poor designs in the ultralight/microlight/homebuilt category - but that applies to pullers as well as pushers. The ones I flew were pretty docile in the air, arguably more so than the Cessna 150, which is a puller and not generally regarded as a high performance tricky airplane. Maybe it’s a matter of having the kinks worked out of the design by now.

A word about the Cessna Skymaster, the C-337 - I’m not an authority but we do have one at my local field. The “critical engine” is, in fact, the rear engine. On the rear engine alone it’s quite controllable and can even produce a useful (although not wonderful) rate of climb. On just the front engine… well, the pilot owner says don’t expect to maintain level flight and it’s just not fun. Now, why that is so I don’t know, but at least in THAT airplane the pusher engine is more important/useful than the puller.

Oh, and parachutes - I know folks who have jumped out of plenty of pushers. This doesn’t seem to be an issue. Any time you jump from an airplane you have to jump away from it as well - hitting the tail of a puller plane can be just as deadly as hitting the prop of a pusher.

17

Those airflow issues you mentioned:

One of the problems with a pusher that doesn’t run a boom out to the tail is that you can’t taper the fuselage. The goal of efficient airplane design is to maintain laminar flow of the air over as much of the airplane as you can. The most efficient shape for doing this is a teardrop, and airplane naturally take on this shape to some extent because the passenger compartment is wide and then it tapers slowly back to the tail.

In a pusher, the fuselage stops abruptly at the engine, and the air detaches and becomes turbulent. This lowers efficiency. In addition, it causes the air going across the tail to be turbulent, but can cause squirrely handling characteristics.

Then there are secondary effects. A few pusher airplanes have a problem where the airflow can detach from the fuselage on one side and not the other when the airplane is being slipped, causing instability in the yaw axis. Sometimes you’ll see vortex generators on the sides of pushers to keep the airflow attached to the fuselage.

18

I remember seeing information about a Japanese WWII fighter that was in development. It had a six-bladed pusher prop, swept-back wings and canards. Very modern looking. I believe it was called Shinden (Lightning)

19

OK, so people have posted a few reasons why pusher prop aircraft is problematic. Is it possible there are more reasons for this?

I ask becuase some of the reasons provided here contradict with the fact that many jet planes (especially fighters) have rear mounted engines (the importance of undisturbed air and laminar flow for example)

20

Everything everyone’s mentioned are valid reasons, but I have to say that, IMO, the chief factor in pusher vs. puller was airframe design. Specifically, engine placement.

In other words, it’s not so much that aircraft makers studied the aerodynamics of push vs. pull and fit the design to that, but the other way round. As aircraft quickly evolved from the Wright Flyer in 1903 to the classic airplane shape we still have today (fuselage, wing, tail etc.) the easiest place to put the prop was on the nose.

Today, almost all ultralights are pushers due to structural rather than aerodynamic concerns. The area where the wing, tail boom and cockpit come together being the strongest part of the airframe makes it the only easy place to mount the engine. And the engine’s position makes it much easier to have it push instead of pull.